Ok, sorry for the delay, but here is the link to the list: http://www.mediafire.com/file/hz2uhrkz98egq68/GTA_V_2001_Retro.txt Cars that aren't included in the list are either too new, or old enough that its obvious the cars where made before 2001.
Some things to consider
- Majority of Vehicles in 2001 had Hubcaps instead of alloy wheels. While GTA V doesn't have Hubcap wheels, try adding certian types low rider wheels to cars such as the Feroci and Merit, since their real life counter parts used hubcaps
- To enhance realism, it would by a good Idea to redesign liveries for some of the buses and trucks in the game to make them look older.